U.S. patent application number 12/088161 was filed with the patent office on 2008-10-16 for regenerable sorbents for removal of sulfur from hydrocarbons and processes for their preparation and use.
This patent application is currently assigned to Research Triangle Institute. Invention is credited to Santosh K. Gangwal, Raghubir Gupta, Brian S. Turk.
Application Number | 20080251423 12/088161 |
Document ID | / |
Family ID | 37900387 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080251423 |
Kind Code |
A1 |
Turk; Brian S. ; et
al. |
October 16, 2008 |
Regenerable Sorbents for Removal of Sulfur from Hydrocarbons and
Processes for Their Preparation and Use
Abstract
A sorbent for use in removing sulfur contaminants from
hydrocarbon feedstocks is provided, wherein the sorbent contains
zinc aluminate in an amount of at least 40 wt % (calculated as
ZnAl.sub.2O.sub.4); free alumina in an amount of from about 5 wt %
to about 25 wt % (calculated as Al.sub.2O.sub.3); and iron oxide in
an amount of from about 10 wt % to about 30 wt % (calculated as
Fe.sub.2O.sub.3); wherein each of the free alumina and iron oxide
are present in non-crystalline form as determined by X-ray
diffraction analysis, and a method for producing the sorbent and
method for using the sorbent to reduce sulfur contaminants in
hydrocarbon feedstocks.
Inventors: |
Turk; Brian S.; (Durham,
NC) ; Gangwal; Santosh K.; (Cary, NC) ; Gupta;
Raghubir; (Durham, NC) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Research Triangle Institute
Research Triangle Park
NC
|
Family ID: |
37900387 |
Appl. No.: |
12/088161 |
Filed: |
September 27, 2006 |
PCT Filed: |
September 27, 2006 |
PCT NO: |
PCT/US2006/037460 |
371 Date: |
March 26, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60720491 |
Sep 27, 2005 |
|
|
|
Current U.S.
Class: |
208/244 ;
208/247; 208/248; 502/406; 502/415; 502/439 |
Current CPC
Class: |
B01J 23/005 20130101;
B01J 20/08 20130101; B01J 35/1014 20130101; C10G 45/02 20130101;
B01J 23/06 20130101; B01J 2220/42 20130101; B01J 20/0244 20130101;
C10G 25/05 20130101; C10G 25/003 20130101; B01J 20/0229 20130101;
B01J 35/1019 20130101; C10G 2300/202 20130101; B01J 20/06 20130101;
C10G 2300/207 20130101 |
Class at
Publication: |
208/244 ;
208/247; 208/248; 502/406; 502/415; 502/439 |
International
Class: |
C10G 25/12 20060101
C10G025/12; B01J 20/02 20060101 B01J020/02 |
Claims
1. A sorbent for use in removing sulfur contaminants from a
hydrocarbon feedstock, comprising: a) zinc aluminate in an amount
of at least about 40 wt % (calculated as ZnAl.sub.2O.sub.4); b)
free alumina in an amount of from about 5 wt % to about 25 wt %
(calculated as Al.sub.2O.sub.3); and c) iron oxide in an amount of
from about 10 wt % to about 30 wt % (calculated as
Fe.sub.2O.sub.3); wherein each of the free alumina and iron oxide
are present in non-crystalline form as determined by X-ray
diffraction analysis.
2. The sorbent of claim 1, wherein the zinc aluminate is present in
an amount of at least 50 wt %.
3. The sorbent of claim 2, wherein the zinc aluminate is present in
an amount of at least 60 wt %.
4. The sorbent of claim 3, wherein the zinc aluminate is present in
an amount of at least 70 wt %.
5. The sorbent of claim 1, wherein the free alumina is present in
an amount of from about 10 wt % to about 20 wt %.
6. The sorbent of claim 1, wherein the iron oxide is present in an
amount of from about 15 wt % to about 25 wt %.
7. The sorbent of claim 1, further comprising up to 20 wt % of one
or more members selected from the group consisting of promoter
components and inert components.
8. The sorbent of claim 1, wherein the sorbent is substantially
free of promoter components and inert components.
9. The sorbent of claim 1, wherein the sorbent has a BET surface
area of at least 50 m.sup.2/g.
10. The sorbent of claim 9, wherein the sorbent has a BET surface
area of at least 80 m.sup.2/g.
11. The sorbent of claim 10, wherein the sorbent has a BET surface
area of at least 100 m.sup.2/g.
12. The sorbent of claim 1, wherein the sorbent has a particle size
of particles or agglomerations of particles of from 40 to 70
microns.
13. The sorbent of claim 1, wherein the sorbent is in a pelletized
form.
14. A method of producing a sorbent, comprising: heating under
oxidizing conditions precipitated precursors of zinc oxide,
aluminum oxide and iron oxide, wherein the precursor for aluminum
oxide is present in a molar excess sufficient to react with
substantially all of the precursor of zinc oxide and to produce
free alumina, and wherein said precipitated precursors of zinc
oxide and iron oxide are present in amounts sufficient that said
sorbent has a composition comprising; a) zinc aluminate in an
amount of at least about 40 wt % (calculated as ZnAl.sub.2O.sub.4);
b) free alumina in an amount of from about 5 wt % to about 25wt %
(calculated as Al.sub.2O.sub.3); and c) iron oxide in an amount of
from about 10 wt % to about 30 wt % (calculated as
Fe.sub.2O.sub.3)
15. The method of claim 14, wherein said precipitated precursors of
zinc oxide, aluminum oxide and iron oxide are Zn(NO.sub.3).sub.2,
Fe(NO.sub.3).sub.3.9H.sub.2O, and Al(NO.sub.3).sub.3,
respectively.
16. The method of claim 14, wherein said heating is at a
temperature of at least 550.degree. C.
17. The method of claim 16, wherein said heating is at a
temperature of at least 650.degree. C.
18. The method of claim 14, wherein said sorbent is in a pelletized
form.
19. The method of claim 18, wherein said pelletized form is
obtained by extrusion of a wet paste formed from said precipitated
precursors.
20. The method of claim 19, wherein said wet paste is obtained by
wetting a dried filter cake of said precipitated precursors with
sufficient liquid to improve flow properties of the paste.
21. The method of claim 20, wherein said wetting is performed with
nitric acid.
22. A method of reducing sulfur contaminants in a hydrocarbon
feedstock, comprising: contacting a hydrocarbon feedstock
containing one or more sulfur containing contaminants, with a
sorbent according to claim 1 in a reactor, at a temperature of from
about 600.degree. F. to about 800.degree. F. under a reducing
atmosphere; and recovering a reduced sulfur hydrocarbon feedstock
having a sulfur content of about 15 ppmw or less.
23. The method of claim 22, wherein said one or more sulfur
containing contaminants are present in said hydrocarbon feedstock
in a total amount of at least 100 ppmw.
24. The method of claim 22, wherein said one or more sulfur
containing contaminants are one or more cyclic or polycyclic
organic sulfur contaminants.
25. The method of claim 24, wherein at least about 90 wt. % of
total organic sulfur contaminant content is composed of cyclic and
polycyclic organic contaminants.
26. The method of claim 22, wherein said hydrocarbon feedstock is
an HDS effluent.
27. The method of claim 22, wherein said hydrocarbon feedstock
comprises H.sub.2S formed during the HDS process.
28. The method of claim 27, wherein said hydrocarbon feedstock
comprises H.sub.2S in an amount up to about 900 ppmw.
29. The method of claim 22, wherein said sorbent is in a pelletized
form.
30. The method of claim 22, wherein said reducing atmosphere is
provided by addition of hydrogen gas to said hydrocarbon feedstock
being fed to the reactor.
31. The method of claim 30, wherein said hydrogen gas is added in
an amount of at least 1000 scf/bbl of hydrocarbon feedstock.
32. The method of claim 22, wherein said contacting is conducted in
a fixed-bed reactor.
33. The method of claim 22, wherein on a periodic basis, the
sorbent is regenerated by contacting the sorbent with an oxygen
containing gas at a temperature of from about 800.degree. F. to
about 1200.degree. F.
34. The method of claim 33, wherein said oxygen containing gas is
air.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to sorbents for the
desulfurization of hydrocarbons, particularly hydrocarbon fuels and
hydrocarbon fuel components and their precursors. More
particularly, the present invention relates to sorbents capable of
removing cyclic and polycyclic sulfur compounds such as
benzothiophenes, dibenzothiophenes, and polybenzothiophenes, and/or
other organic sulfur contaminants including organic sulfides,
disulfides, mercaptans, thiophenes, and the like, from hydrocarbon
fuels such as gasoline, diesel fuels, aviation fuels, and from
components and precursors of such fuels such as FCC naphtha, i.e.,
naphtha from a fluid catalytic cracker (FCC), FCC light cycle oil,
coker distillate, and the like.
BACKGROUND OF THE INVENTION
[0002] International Patent Publication WO02/22763 A1, published
Mar. 21, 2002, (assigned to RESEARCH TRIANGLE INSTITUTE) describes
sulfur removal sorbents and processes for their preparation and
use. The sulfur removal technology and sorbents of WO02/22763 A1
disclose the treatment of hydrocarbon fuels, particularly diesel
and gasoline fuels, to reduce sulfur contaminants to less than
about 30 parts per million by weight (ppmw), for example, to 15
ppmw or less. In particular, a normally liquid hydrocarbon fuel or
fuel component, such as an FCC naphtha, FCC light cycle oil, coker
distillate, straight run diesel fraction, or the like, is treated
at an elevated temperature, preferably a temperature above about
300.degree. C. (572.degree. F.), with a sorbent comprising an
active metal oxide sulfur sorbent, such as a zinc oxide, iron
oxide, zinc titanate or the like, in the absence of an active
hydrodesulfurization (HDS) catalyst, to reduce sulfur contaminant
levels to less than about 30 ppmw, sulfur. The sorbents preferably
include a refractory inorganic oxide cracking catalyst support such
as alumina, an aluminosilicate or the like, in combination with the
metal oxide sulfur sorbent. Metal-substituted inorganic oxide
cracking catalyst support such as metal aluminates, e.g., zinc
aluminate, iron aluminate, are among the preferred supports.
[0003] The desulfurization technology of Patent Publication
WO02/22763 A1 can achieve substantial reductions of cyclic and
polycylic organic sulfur contaminants in various feedstocks such as
hydrotreated FCC naphtha and hydrotreated diesel blends and
components to reduce their sulfur content to below 30 ppmw, or
less, while avoiding or minimizing the problems traditionally
associated with cyclic sulfur contaminant removal. Such traditional
problems have included high hydrogen consumption associated with
olefin and aromatic saturation, product yield losses and/or
increased processing costs associated with HDS processes. In one
embodiment, the sorbents and desulfurization processes of Patent
Publication WO02/22763 A1 are employed in a polishing step for
removal of sulfur contaminants, particularly cyclic and polycylic
organic sulfur contaminants, from relatively low-sulfur feedstocks
including low-sulfur hydrocarbon fuels, fuel components or fuel
precursor feeds.
[0004] Regeneration of the sorbents is achieved by contacting the
sorbent with an oxygen-containing gas, preferably air, at a
temperature sufficient to cause the sulfur present on the sorbent
to react with oxygen to form sulfur dioxide. Typically, the
equilibrium temperatures in the regeneration zone exceed a
temperature of about 425.degree. C. (800.degree. F.).
[0005] The entire disclosure of the aforesaid International Patent
Publication WO02/22763 A1 is hereby incorporated herein.
SUMMARY OF THE INVENTION
[0006] The present invention provides sulfur sorbents which can be
used to remove sulfur contaminants, particularly cyclic and
polycylic organic sulfur contaminants, from hydrocarbon feedstocks
such as hydrotreated FCC naphtha and hydrotreated diesel blends and
components. The sorbents of the invention have high reactivity and
high surface area, and can be prepared in pelletized form in fixed
bed reactors. Advantageously the sorbents are used to perform the
final sulfur removal step in the production of diesel fuels.
[0007] The sulfur sorbents of the invention comprise zinc aluminate
(calculated as ZnAl.sub.2O.sub.4) in an amount of at least about 40
wt. %, preferably at least about 50 wt. %, more preferably from
about 60 wt. % to about 70 wt. %, free alumina (calculated as
Al.sub.2O.sub.3) in an amount ranging from about 5 wt. % to about
25 wt. %, preferably from about 10 to about 20 wt. %, and iron
oxide (calculated as Fe.sub.2O.sub.3) in an amount ranging from
about 10 wt. % to about 30 wt. %, preferably from about 15 to about
25 wt. %. The iron oxide is present in non-crystalline form (i.e.,
no crystalline iron oxide phase is detected by conventional X-Ray
Diffraction (XRD) analysis). Similarly, the free alumina (i.e.,
aluminum oxide that is not reacted with zinc) is also present in
non-crystalline form, (i.e., no crystalline aluminum oxide phase is
detected by conventional XRD analysis). Although currently not
preferred, the sorbent compositions of the invention can optionally
include promoter components and chemically inert components (the
latter including components that may exhibit measurable but only
minimal chemical activity), in amounts of up to 20 wt %, based on
the total weight of the sorbent, preferably less than 10 wt %, more
preferably less than 5 wt % of the total sorbent weight. Sorbent
compositions which are substantially free of such promoters and/or
inert components such as binders or the like are currently
preferred in the practice of the invention.
[0008] The sorbents of the present invention are advantageously
prepared from a mixture of precipitated precursors of zinc oxide,
iron oxide and aluminum oxide, such precursors being known in the
art. The zinc aluminate, iron oxide and free alumina components of
the sorbent are formed when the precursors are heated in an
oxidizing environment. Currently preferred precipitated precursors
of zinc oxide, iron oxide, and aluminum oxide, respectively, are
Zn(NO.sub.3).sub.2, Fe(NO.sub.3).sub.3.9H.sub.2O , and
Al(NO.sub.3).sub.3. The aluminum oxide precursor is present in a
molar amount exceeding the zinc oxide to thereby provide free
alumina in the final sorbent. Advantageously, the precursor mixture
is initially formed as a wet filtered cake recovered directly from
a precipitation step or steps. Preferably, the precipitated
precursors in the precursor mixture are simultaneously formed in a
single co-precipitation step. The filter cake is preferably
pre-dried in one or a plurality of heating steps, preferably in an
oxidizing atmosphere, e.g., air, at sufficiently high temperatures
to convert the precursors to their oxides. The dried filter cake is
remoistened to form a paste, preferably after a grinding step, and
then formed into pellets, preferably by extrusion. Preferably
nitric acid is added to the paste in a small amount sufficient to
improve the flow properties of the paste, prior to extrusion of the
paste. The pellets are heated to a temperature of at least about
550.degree. C., preferably above about 650.degree. C. to form the
final sorbent.
[0009] The sorbents of the invention differ in several aspects from
those disclosed in Patent Publication WO02/22763 A1. The iron oxide
component of the prior sorbents was deposited onto a refractory
support and, following the calcination step, was present as a
crystalline phase. The iron oxide component of the current sorbents
is not present in crystalline form, although the reasons for this
are not currently fully understood. The non-crystalline nature of
the iron oxide is believed to result, at least in part, from the
process used to form the current sorbents, i.e., from the
exceedingly small sizes of the precursors in the precipitated
precursor mixture, and from the simultaneous conversion of the
precursors into the metal oxide components of the sorbent. The
non-crystalline nature of the iron oxide may also be due in part to
an interaction between the iron oxide and the free alumina in the
final sorbent. The sorbents of the invention have an exceedingly
high surface area, typically above about 50 square meters per gram
(m.sup.2/g, measured as BET surface area as will be appreciated by
the skilled artisan), preferably above about 80 m.sup.2/g, more
preferably above about 100 m.sup.2/g, and also have acceptable
crush strength.
[0010] In the prior sorbents, alumina, when used, was present as a
crystalline phase. In the present sorbents, the free alumina is not
present as a crystalline phase. It is also noteworthy that the free
alumina in the current sorbents provides a significant benefit in
the manufacturing process. In particular, the "precipitated
precursor" process initially forms extremely fine precipitates
which are preferably dried prior to conversion into pellets.
However when the precipitate contents of zinc oxide and aluminum
oxide precursors are present in equal molar quantities, (in
combination with the iron oxide precursor), it was found that it
was extremely difficult to remove moisture from the filter cake
prior to drying. The presence of free alumina, due to an unknown
interaction with either the zinc oxide or iron oxide precursor, or
both, provides a filter cake that releases water much more
readily.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] In the foregoing description, and in the following detailed
description, preferred embodiments of the invention are described
to enable practice of the invention. Although specific terms are
used to describe and illustrate the preferred embodiments, such
terms are not intended as limitations on practice of the invention.
Moreover, although the invention is described with reference to the
preferred embodiments, numerous variations and modifications of the
invention will be apparent to those of skill in the art upon
consideration of the foregoing, together with the following
detailed description.
[0012] The quantities of zinc aluminate, iron oxide and free
alumina in sorbents of the invention can be determined by
calculations based on the starting materials, as will be apparent
to the skilled artisan. Alternatively, the quantities of zinc
aluminate, iron oxide and free alumina can be determined from
quantitative analytical procedures to measure the zinc, aluminum,
and iron metal contents of the sorbents as will also be apparent to
the skilled artisan. In either case, weight percent calculations
are determined-wherein the zinc aluminate is calculated as
ZnAl.sub.2O.sub.4, the iron oxide is calculated as Fe.sub.2O.sub.3,
and the free alumina is calculated as Al.sub.2O.sub.3. The term,
"substantially free", is used herein to mean a weight percent of 1
percent or less.
[0013] Detection of crystalline phases in the sorbent are
determined by x-ray diffraction procedures. X-ray diffraction
procedures also allow determination of "crystallite size" using
x-ray diffraction line broadening analysis of the most intense peak
for the crystalline phases, if present. The qualitative data for
this analysis are collected using Cu K.alpha. X-rays generated at
45 kV and 40 mA on a Shimadzu model XRD-6000 outfitted with a
1.degree. divergence slit, a 0.3 mm receiving slit, and a
diffracted beam monochromator, or the equivalent.
[0014] Samples are inspected to ensure that the particles or
agglomerations of particles are between 40 and 70 microns. Samples,
that do not meet these specifications, are ground using a mortar
and pestle with moderate hand pressure for no more than one minute
to reduce and homogenize particle size. Samples are loaded into an
XRD sample holder and the material is packed into the holder as
tightly as possible with hand pressure using a glass slide to
ensure that a flat surface is attained, which is on the same plane
as the surface of the sample holder.
[0015] The XRD pattern is measured with a Shimadzu XRD-6000. This
instrument uses a copper source stimulated with 45 kV and 40 mA to
generate Cu K.alpha. X-rays with a maximum output of 2 kW. These
x-rays pass through a 1.degree. divergence slit. The sample is
scanned from 8 to 62 degrees 2.theta.. The scan rate is 0.02
degrees per 2 seconds. A 3 mm receiving slit and diffracted beam
monochromator process the radiation prior to a sodium iodide
scintillation counter, which measures counts per second. The
operation and data collection of the Shimadzu 6000 is controlled by
Shimadzu XRD-6000 V4.1 software.
[0016] The raw data generated by the Shimadzu XRD-6000 V4.1
software is reformatted by a python language program as suitable
input for software for interpreting and analyzing the XRD
diffraction patterns. The interpretation software is Jade 3.1. One
of the values that is calculated by the Jade software is
crystallite size. The crystallite -size is calculated according to
the formula:
Size (Angstroms)={0.9.times.W/[FWHM-(GW).sup.2].sup.1/2/}/Cos
.theta.
where W, the X-ray wavelength for the Cu source, is 1.540562
angstroms, FWHM is the reported peak width at half maximum in
radians as determined by the software, GW is the inherent
broadening factor for this instrument and theta is half the
reported peak centroid. The final reported crystallite size for
each crystalline phase is the crystallite size calculated by the
Jade software for the most intense peaks.
[0017] Returning now to the sorbents and processes of the
invention, it will be appreciated to those of skill in the art,
that although in the currently preferred embodiments of the
invention, the sorbents are prepared in the form of pelletized,
fixed bed sorbents, the sorbents alternatively can be provided in a
fluidizable form for use in various fluidized reactors and
processes. In such cases, the filter cake of precursors is
preferably converted into a slurry, spray dried, and calcined, as
will be apparent to those of skill in the art.
[0018] As indicated previously the sorbents of the invention can be
used to remove sulfur contaminants, particularly cyclic and
polycylic organic sulfur contaminants, from various hydrocarbon
feed stocks such as hydrotreated FCC naphtha and hydrotreated
diesel blends and the like to provide a final product having a
sulfur content of 15 ppmw or less, preferably 10 ppmw or less. In
one preferred process, the sorbents of the invention are used to
remove cyclic and polycyclic sulfur contaminants from a
hydrodesulfurization (HDS) effluent, which contains H.sub.2S formed
during the HDS process. In this regard, it is noteworthy that
preferred sorbents of the invention are capable of removing cyclic
and polycyclic sulfur compounds in presence of H.sub.2S and
mercaptans.
[0019] According to one particularly preferred process embodiment,
the sorbents of the invention are used to treat a desulfurized
diesel feed stream which is received directly from a conventional
HDS diesel fuel treating process. The HDS diesel effluent, which
contains gaseous H.sub.2S and organic sulfur contaminants, is
preferably passed into a conventional fixed bed apparatus
containing sorbents of the invention in pelletized form, at a
temperature of from about 600.degree. F. to 800.degree. F.
(315.degree. C. to 425.degree. C.), preferably about 700.degree. F.
(370.degree. C.). In general the HDS diesel effluent stream will
have a sulfur exceeding regulatory requirements for the sulfur
content in diesel fuels, for example, a sulfur content above 10
ppmw. Typically the HDS diesel effluent stream fed to the fixed bed
reactor has an organic sulfur contaminant content exceeding 100
ppmw, more typically exceeding 300 ppmw, even more typically, an
organic sulfur content of from 500 to 1000 ppmw. Typically the
organic sulfur contaminant content is composed predominantly of
cyclic and polycyclic organic sulfur contaminants, i.e., at least
about 90 wt. % of the total organic sulfur contaminant content is
composed of cyclic and polycyclic organic contaminants. Preferably,
hydrogen is mixed with the HDS diesel effluent which is fed to the
fixed bed reactor containing the sorbent.
[0020] Preferably the quantity of hydrogen mixed with the HDS
diesel feed stream is an amount of at least about 1000 standard
cubic feet per barrel (scf/bbl) or greater, preferably in an amount
of from about 2000 to about 4000 scf/bbl. The hydrogen prevents or
minimizes coking of the sorbent which typically results from high
temperature hydrocarbon processing. The consumption of hydrogen is
accordingly relatively low. Unreacted hydrogen can be recovered by
conventional separation processes from the desulfurized diesel
which has been contacted with the sorbents of the invention. The
separated hydrogen can then be recycled for mixing with the HDS
diesel effluent which is fed to the fixed bed reactor containing
the sorbent of the invention, and/or for mixing with the feed to
the diesel HDS unit. Following treatment with the sorbents of the
invention, the effluent stream is also preferably treated by
conventional means for removal of various contaminants, such as
light gaseous hydrocarbons, e.g., methane, ethane, propane, etc.,
and/or H.sub.2S and the like.
[0021] A final diesel product is produced according to this
preferred embodiment of the invention, which has an organic sulfur
content of 15 ppmw or less, preferably 10 ppmw or less. The fixed
bed containing the sorbents of the invention is periodically
disconnected from the hydrocarbon feedstream and treated for
regeneration by contacting the sorbent with an oxygen containing
gas, typically air, at a temperature of from about 800.degree. F.
to about 1200.degree. F. (about 425.degree. C. to about 650.degree.
C.), preferably at a temperature of about 800.degree. F. to about
900.degree. F. (about 425.degree. C. to about 480.degree. C.).
[0022] The following examples illustrate preferred sorbents of the
invention and the preferred process for preparing them.
EXAMPLE 1
Preparation of Sorbents
[0023] This example demonstrates preparation of fixed bed sorbents
having the composition; 65 wt % ZiAl.sub.2O.sub.4, 20 wt. %
Fe.sub.2O.sub.3, and 15 wt % Al.sub.2O.sub.3. The sorbents are
prepared by the co-precipitation method under a constant pH of
6.+-.0.2 using a mixture of aqueous solutions of zinc (II) nitrate,
aluminum (III) nitrate and iron (III) nitrate as metal precursors
and aqueous NH.sub.3 as a precipitating agent. The concentrations
of Zn, Al and Fe in their nitrate solutions are 16.6, 4.3 and 7.0%,
respectively. For the preparation of 75 lb of the final oxide
mixture, 104 lb of zinc nitrate solution, 471 lb of aluminum
nitrate solution, and 150 lb of iron nitrate solution are mixed in
tank-1. In another tank (tank-2), 245 lb of 29% ammonia was mixed
with 245 lb of de-ionized (DI) water. The contents in tank-1 and
tank-2 are pumped and mixed in a tank-3 at room temperature under
vigorous stirring using an agitator. The flow rate of the mixed
metal solutions in tank-1 is set at 10-15 lb/min. while adjusting
the flow rate of NH.sub.3 solution in order to maintain the pH of
the precipitate to 6.+-.0.2. The precipitate is aged at room
temperature for about 30 min. and then filtered using a filter
press. The cake is air blown for 15 min after filtration, dropped
into a re-slurry tank, mixed with DI water to re-slurry the wet
cake and the filtration is repeated to reduce residual ammonia. The
cake is then pre-dried in a muffle furnace at 220.degree. C.
(428.degree. F.) for 2 hours.
[0024] Extrudates of fixed bed diesel desulfurization sorbents are
prepared using this cake by grinding and mixing with an appropriate
amount of DI water and HNO.sub.3 as a binder and extruding the
paste. Typically, 2060 g of the cake is used as is or pre-dried at
370.degree. C. The cake is then ground to powder in a mechanical
mixer. To this powder, 932.1 g of DI water containing 45.1 g of
concentrated HNO.sub.3 is added dropwise to achieve a moisture
content of around 36 wt % while grinding the powder. The paste is
then extruded on a 2.25 inch Bonnet extruder using both a 1/16 inch
as well as a 1/8 inch die. All extrudates are calcined at
650.degree. C. for 2 h at a ramp rate of 3.degree. C./min. This
procedure is used to prepare a number of distinct samples by
varying the amount of DI water and concentrated HNO.sub.3 as well
as extrusion size used. Table 1 summarizes the amount of DI water
and concentrated HNO.sub.3 used for the preparation of a series of
extrudates while their physical properties are shown in Table 2.
XRD analysis showed only a zinc aluminate crystalline phase, with a
crystallite size of 95 .ANG. to 105 .ANG.. Free zinc oxide, iron
oxide, or aluminum oxide crystalline phases were not detected. In
addition, iron aluminate could not be detected.
TABLE-US-00001 TABLE 1 Summary of Sorbent Preparations Pre- calc.
Wt of Wt of DI Wt of Moisture HNO.sub.3 Extrusion Temp. Solid water
HNO.sub.3 content content size Sample code (.degree. C.) (g) (g)
(g) (wt %) (wt %) (inch) 022105a-DDS 220 2000 464 37 42.62 1.03
1/16 022505a-DDS 370 2300 1024 51.6 36.84 1.06 1/8 022805a-DDS 370
1900 843.1 42.5 36.77 1.06 1/8 022805b-DDS 370 1900 843.1 42.5
36.77 1.06 1/16 031805a-DDS 370 2060 887 45.1 36.20 1.05 1/16
TABLE-US-00002 TABLE 2 Physical Properties of Sorbents Physical
Properties CS.sup.$ CBD.sup.# (lbs. BET SA Porosity* Av. Pore
Sample code (g/cc) force) (m.sup.2/g) (%) dia (.ANG.)* 022105a-DDS
0.76 3.28 92 44.4 84 022505a-DDS 0.88 22.83 99 47.4 89 022805a-DDS
0.82 12.11 106 46.8 82 022805b-DDS 0.77 6.83 108 48.6 84
031805a-DDS 0.89 -- 87.6 54.1 117 .sup.#Compact bulk density
.sup.$CS = Crush strength *Determined by Hg porosimetry
EXAMPLE 2
Desulfurization of Hydrotreated Diesel, with Sorbent of Example
1
[0025] Approximately 237.2 g of the extruded sorbent sample from
batch 022105a-DDS of Example 1 was loaded in a bench-scale reactor
system. This sample was initially tested in eight alternating
desulfurization and regeneration cycles. In each of the
desulfurization cycles, the sample was exposed to a vapor mixture
of hydrogen and hydrotreated diesel containing 4400 scf of hydrogen
per bbl of hydrotreated diesel at 700.degree. F. and 30 psig for 2
hours. In the regeneration cycles, the sample was contacted with a
mixture of 2 vol % O.sub.2 in N.sub.2 at 700.degree. F. and 30 psig
until the CO.sub.2 concentration in the effluent was <500 ppmv.
During the desulphurization cycles, the sulfur in the hydrotreated
diesel feed was 148 ppmw, whereas the sulfur in the effluent
product was consistently below 50 ppmw for a majority of the 2 hour
exposure period. The sorbent was then tested for three additional
desulfurization cycles during which 900 ppmv of H.sub.2S was added
to the hydrogen and hydrotreated diesel mixture fed to the sorbent.
The sorbent successfully reduced the sulfur in the hydrotreated
diesel feed from 148 ppmw to less than 50 ppmw for most of each of
the 2 hour exposure periods despite the H.sub.2S gas in the
feed.
EXAMPLE 3
Desulfurization of Hydrotreated Diesel with Sorbent of Example
1
[0026] A 237.2 g sample of the 022105a-DDS sorbent sample prepared
in Example 1 was loaded in a bench-scale reactor system. The
sorbent was initially conditioned for 12 alternating
desulfurization and regeneration cycles. In the initial
desulfurization cycles, the sorbent was contacted with a mixture of
hydrogen and hydrotreated diesel vapor containing 4400 scf of
hydrogen/ bbl of hydrotreated diesel at 700.degree. F. and 30 psig
for 2 hours. In the initial regeneration cycles, the sorbent was
contacted with a mixture of 2 vol % O.sub.2 in N.sub.2 until the
CO.sub.2 effluent concentration dropped below 500 ppmv. Subsequent
desulfurization and regeneration cycles were then conducted under
the same conditions except that the ratio of hydrogen to
hydrotreated diesel vapor in the feed was varied. The effluent
product was analyzed for sulfur using an ANTEK 9000 series total
sulfur analyzer and ASTM D 1319 for aromatic content. The results
from this parametric testing are provided in Table 3.
TABLE-US-00003 TABLE 3 Analysis of Aromatic Content of Product
Samples during Parametric Testing Hydrogen to diesel ratio
(scf/bbl) Diesel feed 1132 4392 12984 Aromatics (LV %) 35.6 36.1
35.3 33.4 Olefins (LV %) 1.3 1.7 1.6 2.2 Saturates (LV %) 63.1 62.2
63.1 64.4 Avg S 148 90 40 15 Conc. (ppmw)
As will be apparent to the skilled artisan, the various operating
parameters of pressure, temperature, residence time, hydrogen to
hydrocarbon ratio, etc., can be optimized to obtain a final sulfur
content of or below 10 ppmw.
[0027] The present application is based on and claims priority to
U.S. Provisional application Ser. No. 60/721,491, filed Sep. 27,
2006, the entire contents of which are hereby incorporated by
reference.
* * * * *